<!DOCTYPE html>
<html>
<head>
</head>
<body>
<h1 id="jeden"> nadpis
</h1>
<p>text</p>
<button onclick="vypis()">Tu bude button</button>
<br>
<button onclick="vypis()">Tu bude button
h1</button>
<script>
function vypis() {
document.write('<h1>Tu bude nieco napisane</h1>');
}
</script>
<script>
function zmenah1(){
document.getElementById('jeden').style.fontSize = '50px';
document.getElementById('jeden').style.color = 'red';
}
</script>
</body>
</html>